1. Field of the Invention
This invention relates to an improvement in indirect/direct evaporative cooling devices, and particularly to indirect/direct evaporative cooling devices used in conditioning air for comfort purposes.
2. Description of Related Art
Two stage evaporative coolers offer great promise for satisfying residential cooling loads at lower cost and with reduced environmental impacts compared to conventional air conditioning systems. Two stage coolers include an "indirect" stage and a "direct" stage and are also known as indirect/direct evaporative cooling (IDEC) units. IDEC units provide cooling with much less addition of moisture to the indoor space than direct evaporative coolers. In drier climates, most conventional (vapor-compression cycle) air conditioning systems use energy unnecessarily to remove moisture from indoor spaces.
In the first, i.e. indirect, stage of the IDEC unit, outdoor air is cooled without adding moisture. Indirect cooling is typically accomplished by passing the air through a first set of alternating passages in a system of parallel heat exchange plates. Simultaneously, a second airstream is passed through the second set of alternating passages. Water is supplied to the surfaces of the heat exchange plates that form the second set of passages. The second airstream contacts the wet heat exchange plates and evaporatively cools the plates. The first airstream is cooled by contact with the surfaces of the cooled plate. The cooled first airstream exits the indirect evaporative cooling stage and is then further evaporatively cooled by direct contact with a wet medium in the direct evaporative cooling stage. The first airstream exits the direct cooling stage where it is then supplied to the interior of a building. While it is theoretically possible to cool the supply air completely by an indirect process, the cost of larger plates and greater "wet passage" air quantities limits the potential cost-effectiveness of "indirect-only" coolers.
Several IDEC systems are currently available for commercial building applications. Only one, the "MasterCool 2 Stage" unit produced by AdobeAir of Phoenix, Ariz., is currently marketed for residential applications. "MasterCool 2 Stage" units have been successfully used in many homes. Extensive monitoring data and occupant responses testify to the effective performance of these units. However, these units are somewhat larger than conventional cooling systems. Consequently, the potential for retrofit installations is limited.
In addition, the on/off operation of the blowers of the conventional IDEC systems produces noticeable noise during operation. Consequently, the user is always aware of unit operation.
Moreover, the conventional IDEC systems have the indirect and direct stages formed as independent units that are connected together to form the IDEC unit. Such an arrangement leads to redundancies in the components of the indirect and direct cooling stages. For example, the conventional IDEC systems have separate pumps and blowers for each of the cooling stages. Consequently, such systems are large and expensive.
In addition, the sump of conventional IDEC systems is conducive to bacterial growth which can lead to odors and possible health hazards, because the conventional sump maintains a constant water level. Bacterial growth is fostered by permitting the water to remain in the sump for an extended period of time, particularly during warm weather.
Further, in order to supply the cooled air from the IDEC unit through an exterior wall of the building, it is frequently necessary to modify the wood framing arrangement of the wall. As a result, installation costs are significantly increased.
For these reasons, there exists a need for an indirect/direct evaporative cooling unit that is compact and can be easily retrofitted to existing residences. In addition, there exists a need for an indirect/direct evaporative cooling unit that minimizes awareness of unit operation. There also exists a need for an indirect/direct evaporative cooling unit that can be easily fabricated with a minimum number of components.